Isolation And Screening Of Phosphate-solubilizing Bacteria And The Effect On Phosphorus Release From The Sediments In Rongcheng Swan Lake

Microorganism is an important factor affecting phosphorus release from the sediments,and phosphorus-solubilizing bacteria play a key role in the geochemical cycle of phosphorus.The aims of this study are to study the degree of endogenous pollution in sediments of Swan Lake,and to provide theoretical basis for the control of lake eutrophication.Through the combination of field investigation and indoor simulation,the differences in bacterial community composition in sediments between the algae outbreak area and the non-outbreak area in Swan Lake were analyzed.The organic phosphate-solubilizing strains were screened and identified from the surface sediments of Swan Lake.The phosphate-solubilizing abilities of microorganisms and different phosphate-solubilizing strains from the sediments at different lake areas were analyzed,and the effects of microorganisms,organic phosphate-solubilizing bacteria and algae on the release of nutrients from the sediments were discussed.The main results are as follows:(1)Bacterial community composition in sediments of Swan LakeProteobacteria,Desulfobacterota,Bacteroidetes and Chloroflexi were the dominant bacterial categories in the sediments of Swan Lake.Among them,the bacteria with phosphorus-solubilizing ability accounted for a large proportion.The potential phosphorus-solubilizing ability of the sediments was strong.There were significant differences in bacterial community composition between the sediments of the northwest and south of the lake.At phylum level,Firmicutes,Chloroflexi and Cyanobacteria in the northwestern area with algae outbreak were significantly higher than those in the southern non-outbreak area,while the relative abundance of Proteobacteria in the latter sediment was higher(24.22%?27.58%).(2)Screening and identification of organic phosphate-solubilizing bacteria in sedimentsThe phosphate-solubilizing strains were screened by plate culture method,and then purified several times.A total of 11 strains of organic phosphate-solubilizing bacteria(OPB)were screened from the sediments,of which 4 strains were from the northwestern lake and 7 strains were from the central lake.The diameter ratio of phosphorus dissolving circle ranged from 1.05 to 4.11,among which OPB10 had the highest diameter ratio.It was preliminarily determined that the phosphorus dissolving ability of OPB10 was strong.The 11 strains were sequenced and identified as Bacillus sp,except that OPB3 belonged to Geobacillus sp.Subsequently,six representative strains were selected for the study of phosphate-solubilizing characteristics through shaking flask culture.The soluble phosphorus(SRP)concentration varied from 0.822 mg·L^-1to 30.993 mg·L^-1,and OPB11had the strongest phosphate-solubilizing ability.The phosphate-solubilizing ability of OPB10 decreased with the increasing passage times.(3)Effects of algal decomposition and microorganisms on nitrogen and phosphorus release from the sedimentsThe decomposition of algae and microbial activities changed the physico-chemical properties at the water-sediment interface of Swan Lake.Algal decomposition and microbial activity had significant effects on nitrogen and SRP concentrations in water.The effects of three factors on water nitrogen and phosphorus concentrations followed the order:algae>microorganisms>sediments.The concentrations of TN and TP in water were higher in the non-sterilization treatments than those in the sterilization treatments,which was much higher under the condition with algae than those under the non-algae condition.In addition,the difference in TN and TP concentrations among different microbial treatments in the condition with algae was greater than that in the non-algae condition.Under the condition of algae,the order of water phosphorus concentration was northwest>lake center>south,which was lake center>northwest>south under the condition without algae.The release ability of nutrients from the sediments in the lake center was greatly affected by microbial activities.The release potential of nitrogen and phosphorus in sediments was large in the northwest and the center of the lake where there are a large number of algae and high microbial activity,which should be paid enough attention during the period of algal degradition.(4)Effect of organic phosphate-solubilizing bacteria on phosphorus release from sedimentThrough the shaking flask culture,it was found that the phosphate-solubilizing ability of microorganisms in different lake sediments was significantly different.The SRP concentrations in the culture medium varied from 0.71 mg·L^-1to 44.16 mg·L^-1.The concentration of SRP in S1(northwest)and S6(south)treatments was high.The peak value of SRP concentration at S6 culture medium was 44.16 mg·L^-1,which was about 10times of the initial value.At S1 culture medium,it peaked at 38.03 mg·L^-1,about 6.5 times of the initial value.The microbial phosphate-solubilizing ability of sediments in these two regions was strong.The organic phosphorus concentration in sediments in the northwestern lake was high,therefore its release potential is large.The inoculation simulation experiment of phosphate-solubilizing bacteria showed that the concentrations of TP and SRP in water at different treatments both followed the order of organic phosphate-solubilizing bacteria>indigenous microorganisms>sterile condition at the early stage.Microorganisms could promote the release of phosphorus from the sediments,and the phosphate-solubilizing ability of organic phosphate-solubilizing bacteria was higher than that of indigenous microorganisms in sediments.